The present invention relates generally to microlaser assemblies and, more particularly, to microlaser assemblies having microresonators, one or more electro-optic components and a beam steering element for controllably aligning the laser signals emitted by the microresonator with the electro-optic components.
Modern electro-optical applications are demanding relatively inexpensive, miniaturized lasers capable of producing a series of well-defined output pulses. As such, a variety of microlasers have been developed that include a microresonator and a pair of at least partially reflective mirrors disposed at opposite ends of the microresonator to define a resonant cavity therebetween. The microresonator of one advantageous microlaser includes an active gain medium and a saturable absorber that serves as a Q-switch. See, for example, U.S. Pat. No. 5,394,413 to John J. Zayhowski which issued on Feb. 28, 1995 and U.S. Pat. No. 6,072,815 to Brian L. Peterson which issued on Jun. 6, 2000, the contents of both of which are incorporated in their entirety herein. By appropriately pumping the active gain medium, such as with a laser diode, the microresonator will emit a series of pulses having a predetermined wavelength, pulse width and pulse energy.
As known to those skilled in the art, the wavelength of the signals emitted by a microlaser is dependent upon the materials from which the active gain medium and the saturable absorber are formed. In contrast, the pulse width of the laser pulses emitted by a conventional microlaser is proportional to the length of the resonator cavity. As such, longer resonator cavities will generally emit output pulses having greater pulse widths as defined by the following equation:       t    pw    =            2      ⁢      n      ⁢              xe2x80x83            ⁢      l        c  
in which tpw is the pulse width, 1 is the length of the resonator cavity, n is the refractive index of the microlaser and c is the speed of light. Further, both the pulse energy and average power provided by a microlaser are proportional to the pulse width of the pulses output by the microlaser. All other factors being equal, the longer the microresonator cavity, the longer the pulse width and the greater the pulse energy and average power of the resulting laser pulses as a result of the increased gain.
Conventional microlasers, such as those described by U.S. Pat. No. 5,394,413, are end pumped in a direction parallel to the longitudinal axis defined by the resonator cavity. In this regard, the longitudinal axis of the microresonator cavity extends lengthwise through the resonator cavity and is oriented so as to be orthogonal to the pair of at least partially reflective mirrors that define the opposed ends of the resonant cavity. As such, conventional microlasers are configured such that the pump source provides pump signals in a direction perpendicular to the at least partially reflective mirrors that define the opposed ends of the resonant cavity. The effective length of the resonator cavity is therefore equal to the physical length of the resonator cavity.
While a microlaser can be fabricated such that the resonator cavity has different lengths, a number of factors contribute to generally limit the permissible length of the resonator cavity. In particular, a number of electro-optical applications require microlasers that are extremely small. As such, increases in the length of the resonator cavity are strongly discouraged in these applications since any such increases in the length of the microresonator cavity would correspondingly increase the overall size of the microlaser. In addition, the length of passively Q-switched microlasers is effectively limited by the requirement that the inversion density must exceed a predetermined threshold before lasing commences. As the physical length of the resonator cavity increases, greater amounts of pump energy are required in order to create the necessary inversion density for lasing. In addition to disadvantageously consuming more power to pump the microlaser, the increased pumping requirements create a number of other problems, such as the creation of substantially more heat within the microlaser which must be properly disposed of in order to permit continued operation of the microlaser.
As such, side-pumped microlasers have been developed as described by U.S. patent application Ser. No. 09/337,432, filed Jun. 21, 1999, by Brian L. Peterson, et al. and U.S. patent application Ser. No. 09/337,716 filed Jun. 21, 1999, by Steve Guch, Jr., et at, the contents of both of which are incorporated in their entireties herein. Like an end-pumped microlaser, a side-pumped microlaser includes a microresonator consisting of an active gain medium and a saturable absorber that serves as a Q-switch, and a pair of at least partially reflective mirrors disposed at opposite ends of the microresonator to define a resonant cavity. Unlike an end-pumped microlaser in which the opposed end faces of the microresonator are perpendicular to the longitudinal axis defined by the microresonator, however, the opposed end faces of the microresonator of a side-pumped microlaser are disposed at a non-orthogonal angle, such as between about 30xc2x0 and about 35xc2x0 relative to a line perpendicular to the longitudinal axis defined lengthwise through the microresonator. As such, the microresonator will support a zig-zag resonation pattern. In order to initiate the resonation, the microlaser also includes a pump source for .introducing pump signals into the active gain medium via a side surface of the microresonator. In response to the pumping of the active gain medium via the side surface, the zig-zag resonation pattern is established within the resonant cavity and a series of pulses are emitted once the necessary inversion density has been reached. As a result of the zig-zag resonation pattern, the effective length of the microresonator of a side-pumped microlaser is increased without having to increase the physical dimensions. Thus, a side-pumped microlaser can generate pulses having greater pulse widths and correspondingly greater pulse energies and average power levels than the pulses provided by end-pumped microlasers of a similar size.
Notwithstanding the advantages offered by side-pumped microlasers, some modern electro-optical applications require pulses that have greater pulse energies and greater average power levels as well as pulses that have different wavelengths than that emitted by a microresonator. As such, microlaser assemblies generally include a microresonator and one or more electro-optic components for receiving the pulses and for modifying the pulses. For example, the electro-optic components can include an optical parametric amplifier for amplifying the pulses. Alternatively, the electro-optic components can include one or more non-linear crystals for altering the wavelength of the pulses, such as by doubling or quadrupling the frequency of the pulses.
In order to appropriately receive and modify the pulses emitted by the microlaser, the electro-optic components must be precisely aligned with the microlaser. As the microlaser and the associated electro-optic components become smaller, this alignment becomes even more necessary, but also more difficult. Moreover, as the requirements for microlaser assemblies increase, the proper alignment of the microlaser and the associated electro-optic components becomes even more critical. Thus, a need exists for microlaser assemblies having microresonators and associated electro-optic components that can be reliably aligned in a precise manner in order to provide the output required by modern electro-optical applications.
A microlaser assembly is therefore provided that includes a microresonator having an active gain medium and a passive Q-switch, a pump source for inducing resonation of the microresonator and the generation of laser signals, one or more electro-optic components, such as one or more non-linear crystals, amplifiers, oscillators or other active gain mediums, for modifying the laser signals emitted by the microlaser and a beam steering element for aligning the laser signals emitted by the microresonator with the electro-optic components. In one advantageous embodiment, the pump source pumps the active gain medium via a first side surface of the microresonator. In order to support a zig-zag resonation pattern in response to the side pumping, the first and second end faces of the microresonator are typically disposed at a nonorthogonal angle relative to the longitudinal axis defined by the microresonator. As a result of the zig-zag resonation pattern, the microresonator can generate pulses having greater pulse widths and correspondingly greater pulse energies and average power levels than the pulses produced by conventional microresonators of a similar size. In addition, by precisely aligning the laser signals emitted by the microresonator with the electro-optic components, the beam steering element of the microlaser assembly of the present invention facilitates the reliable and efficient operation of the microlaser assembly and supports multiple downstream electro-optic stages for amplifying the laser signals and/or altering the wavelength of the laser signals depending upon the requirements of a particular application.
Preferably, the beam steering element is controllably adjustable so as to precisely align the laser signals emitted by the microresonator with an electro-optic component. For example, the beam steering element can include at least one wedge prism and, in one embodiment, includes a pair of steering Risley prisms. The beam steering element typically provides for the relatively precise alignment of the laser signals emitted by the microresonator with the electro-optic components. In order to provide more general alignment, the microlaser assembly can also include a mechanical alignment member.
In this advantageous embodiment, the microlaser assembly can include a first mechanical alignment member for aligning the microresonator and the beam steering element and a second mechanical alignment member for aligning the beam steering element and the electro-optic component. For example, the first and second mechanical alignment members can each include at least one pin for operably engaging the microresonator, the beam steering element and/or the electro-optic components. In this regard, the microlaser assembly can further include a microresonator mount for supporting the microresonator and a component mount for supporting the electro-optic component. In addition, the microlaser assembly of this embodiment can include a housing for holding the beam steering element. As such, the at least one pin of the first mechanical alignment member can engage the microresonator mount and the housing for generally aligning the microresonator and the beam steering element. Likewise, the at least one pin of the second mechanical alignment member can engage the component mount and the housing for generally aligning the electro-optic component and the beam steering element. As such, the mechanical alignment members can provide general alignment of the microresonator with the electro-optic components, while the controllably adjustable beam steering element provides more precise alignment or fine tuning.
In one advantageous embodiment in which the microresonator is side-pumped, the microresonator also has a second side surface extending between the opposed end faces and opposite the first side surface. As such, the zig-zag resonation pattern includes a number of segments of alternately opposite slope that intersect at respective inflection points proximate one of the first and second side surfaces. As such, the microlaser assembly can include first and second pump sources for introducing pump signals into the active gain medium at locations along the first and second side surfaces, respectively, that coincide with the inflection points. As such, the gain provided by the pump signals can be maximized.
The microlaser assembly of the present invention therefore provides for the alignment of the microresonator, such as a side-pumped microresonator, with one or more electro-optic components, such as one or more non-linear crystals, amplifiers and oscillators. In particular, the microlaser assembly of one embodiment provides for both the general alignment of the microresonator and the electro-optic component by means of one or more mechanical alignment members, as well as the more precise and controllably adjustable alignment of the microresonator and the electro-optic component by means of a beam steering element. Thus, the laser signals emitted by the microresonator can be efficiently coupled to the electro-optic components in order to provide the desired laser output.